Transaxle for lawn tractor

ABSTRACT

A transaxle is provided for a lawn tractor. The lawn tractor includes a prime mover, a mower unit having a grass-discharging duct disposed at a substantially lateral center portion of the mower unit, left and right drive wheels disposed on lateral opposite sides of the grass-discharging duct, and left and right final transmission devices disposed on lateral opposite sides of the grass-discharging duct. The transaxle is disposed above the grass-discharging duct. The transaxle comprises: a transaxle housing; an input shaft having a lower portion extended downward from the transaxle housing; an input pulley provided on the lower portion of the input shaft so as to be disposed between the transaxle housing and the grass-discharging duct; and left and right output shafts projecting laterally from the transaxle housing opposite to each other so as to be drivingly connected to the respective left and right drive wheels through the respective left and right final transmission devices.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a transaxle disposed above a grass-dischargingduct of a mower unit equipped on a lawn tractor.

2. Related Art

As disclosed in U.S. Pat. No. 6,390,227, there is a conventionalwell-known rear discharge lawn tractor equipped with a mower unitincluding a mower deck and a grass-discharging duct. The mower deck isprovided with rotary blades and a blower which blows grass mowed by therotary blades into the duct. A grass collection box is disposed behind arear end of the lawn tractor and connected to the duct so as to catchgrass sent from the mower deck through the duct.

In the conventional rear discharge lawn tractor, left and right drivewheels are disposed on left and right sides of the duct. A transaxlehaving left and right lateral output shafts is disposed on one lateralside of the duct. Left and right final transmission devices (e.g.,chains and sprockets, belts and pulleys, or gears) are disposed onrespective lateral opposite sides of the duct so that each of the finaltransmission devices is drivingly interposed between the output shaftand the drive wheel. The transaxle includes a transaxle housing, whichincorporates a hydraulic pump, a hydraulic motor fluidly connected tothe hydraulic pump, and the left and right output shafts driven by thehydraulic motor.

Further, the conventional rear discharge lawn tractor is equipped withan engine having a vertical output shaft, and the transaxle includes avertical input shaft (serving as a pump shaft of the hydraulic pump)projecting upward from the transaxle housing. An input pulley isprovided on an upper portion of the input shaft projecting upward fromthe transaxle housing so as to be drivingly connected to a pulleyprovided on the vertical output shaft of the engine through a belt.

Since the transaxle housing has to be low as to ensure a space for theinput shaft with the input pulley projecting upward from the transaxlehousing, the transaxle housing is laterally offset from the duct (i.e.,disposed on one lateral side of the duct as mentioned above) so as to beprevented from interfering with the duct, thereby restricting thelateral width of the duct. Further, a lateral shaft extended from theoutput shaft of the transaxle to one of the left and right finaltransmission devices is passed through a space above the duct, therebyrestricting the vertical width of the duct. Consequently, thegrass-discharging duct of the conventional lawn tractor is restricted involume, thereby restricting the grass discharging (collection) speed ofthe mower unit.

If the transaxle is disposed above the grass-discharging duct, theproblem regarding the restriction of the lateral width of the duct issolved. However, another problem arises because the input pulley on theinput shaft projecting upward from the transaxle housing becomes toohigh to be drivingly connected to the pulley on the engine output shaftthrough a horizontal belt.

SUMMARY OF THE INVENTION

An object of the invention is to provide a transaxle for a lawn tractor,which can increase the volume of a grass-discharging duct of a mowerunit, thereby increasing the grass discharging (or collecting) speed ofthe mower unit.

To achieve the object of the invention, a transaxle is provided for alawn tractor. The lawn tractor includes a prime mover, a mower unithaving a grass-discharging duct disposed at a substantially lateralcenter portion of the mower unit, left and right drive wheels disposedon lateral opposite sides of the grass-discharging duct, and left andright final transmission devices disposed on lateral opposite sides ofthe grass-discharging duct. The transaxle is disposed above thegrass-discharging duct. The transaxle comprises: a transaxle housing; aninput shaft having a lower portion extended downward from the transaxlehousing; an input pulley provided on the lower portion of the inputshaft so as to be disposed between the transaxle housing and thegrass-discharging duct; and left and right output shafts projectinglaterally from the transaxle housing opposite to each other so as to bedrivingly connected to the respective left and right drive wheelsthrough the respective left and right final transmission devices.

Since the lower portion of the input shaft with the input pulleyprojects downward from the transaxle housing so as to receive power froma prime mover, the transaxle housing is able to be disposed above thegrass-discharging duct, thereby enabling the grass-discharging duct tobe laterally expanded so as to increase its volume, and therebyincreasing the grass discharging (collection) speed of the mower unit.In addition, the input pulley on the lower portion of the input shaft islow enough as to be drivingly connected to a pulley on a vertical outputshaft of a prime mover through a substantially horizontal belt, therebyensuring a sufficient efficiency of transmitting power between the primemover and the transaxle.

Preferably, the transaxle further comprises a hydraulic pump and ahydraulic motor. The hydraulic pump is disposed in the transaxle housingso as to be driven by rotating the input shaft. The hydraulic motor isdisposed in the transaxle housing so as to be fluidly connected to thehydraulic pump and to drive the left and right output shafts. Therefore,when the lawn tractor is hydraulically driven by the transaxle, a largevolume of the grass-discharging duct is ensured.

Preferably, a cooling fan is provided on the lower portion of the inputshaft so as to be disposed between the transaxle housing and thegrass-discharging duct. Therefore, a dead space around the lower portionof the input shaft is effectively used for arranging the cooling fanwhile ensuring the above advantages.

Alternatively, preferably, the input shaft has an upper portion extendedupward from the transaxle housing, and a cooling fan is provided on theupper portion of the input shaft so as to be disposed above thetransaxle housing. Therefore, the space between a bottom of thetransaxle and the grass-discharging duct for arranging the input pulleycan be reduced so as to enable the vertical width of thegrass-discharging duct to be further increased.

Another object of the invention is to provide a lawn tractor, which canincrease the volume of a grass-discharging duct of a mower unit, therebyincreasing the grass discharging (or collecting) speed of the mowerunit.

To achieve the other object of the invention a lawn tractor comprises: aprime mover; a mower unit having a grass-discharging duct disposed at asubstantially lateral center portion of the mower unit; left and rightdrive wheels disposed on lateral opposite sides of the grass-dischargingduct; and left and right final transmission devices disposed on lateralopposite sides of the grass-discharging duct. A transaxle is disposedabove the grass-discharging duct. The transaxle comprises: a transaxlehousing; an input shaft having a lower portion extended downward fromthe transaxle housing; an input pulley provided on the lower portion ofthe input shaft so as to be disposed between the transaxle housing andthe grass-discharging duct; and left and right output shafts projectinglaterally from the transaxle housing opposite to each other so as to bedrivingly connected to the respective left and right drive wheelsthrough the respective left and right final transmission devices.

Preferably, the transaxle further comprises a hydraulic pump and ahydraulic motor. The hydraulic pump is disposed in the transaxle housingso as to be driven by rotating the input shaft. The hydraulic motor isdisposed in the transaxle housing so as to be fluidly connected to thehydraulic pump and to drive the left and right output shafts. Therefore,when the lawn tractor is hydraulically driven by the transaxle, a largevolume of the grass-discharging duct is ensured.

Preferably, a cooling fan is provided on the lower portion of the inputshaft so as to be disposed between the transaxle housing and thegrass-discharging duct. Therefore, a dead space around the lower portionof the input shaft is effectively used for arranging the cooling fanwhile ensuring the above advantages.

Alternatively, preferably, the input shaft has an upper portion extendedupward from the transaxle housing, and a cooling fan is provided on theupper portion of the input shaft so as to be disposed above thetransaxle housing. Therefore, the space between a bottom of thetransaxle and the grass-discharging duct for arranging the input pulleycan be reduced so as to enable the vertical width of thegrass-discharging duct to be further increased.

These, further and other objects, features and advantages will appearmore fully from the following description with reference to theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic side view of a rear discharge lawn tractorequipped with a transaxle according to a first embodiment.

FIG. 2 is a schematic plan view of the lawn tractor equipped with thetransaxle according to the first embodiment.

FIG. 3 is a sectional rear view of the lawn tractor equipped with thetransaxle according to the first embodiment, showing the transaxle andleft and right final transmission devices surrounding agrass-discharging duct.

FIG. 4 is a schematic side view of the lawn tractor equipped with atransaxle according to a second embodiment.

FIG. 5 is a sectional rear view of the lawn tractor equipped with thetransaxle according to the second embodiment, showing the transaxle andleft and right final transmission devices surrounding agrass-discharging duct.

FIG. 6 is a sectional plan view of the transaxle according to either thefirst and second embodiment.

FIG. 7 is a sectional side view of the transaxle according to the firstembodiment shown in FIGS. 1 to 3.

FIG. 8 is a sectional side view of the transaxle according to the secondembodiment shown in FIGS. 4 and 5.

FIG. 9 is a cross sectional view taken in XI-XI line of either FIG. 7 or8.

FIG. 10 is a cross sectional view taken in XI-XI line of either FIG. 7or 8 when the transaxle is provided with an alternative structure of acharge pump.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 1 to 3 illustrate a rear discharge lawn tractor equipped with atransaxle RT according to a first embodiment, and FIGS. 4 and 5illustrate a rear discharge lawn tractor equipped with a transaxle RTaccording to a second embodiment. FIG. 2 is representative as asectional plan view of the lawn tractor equipped with transaxle RTaccording to the second embodiment on the assumption that an alternativecooling fan 20 b is disposed above a rear transaxle housing 10.

A common general structure of the rear discharge lawn tractor sharedbetween the first and second embodiments will be described withreference to FIGS. 1 to 5. The rear discharge lawn tractor has a bodyframe 1 formed integrally with a horizontal plate 1 a and vertical sideplates 1 b extended downward from front, rear, left and right edges ofhorizontal plate 1 a.

As shown in FIG. 2, a vertically penetrating opening 1 e is formed in afront portion of horizontal plate 1 a of body frame 1. A vertical outputshaft type engine 2 is attached onto an upper surface of horizontalplate 1 a around opening 1 e through vibration-isolating members 2 e soas to be mounted upright from horizontal plate 1 a of body frame 1. Afuel tank 2 f is fixed on a rear portion of engine 2, and a muffler 2 gis extended forward from engine 2.

As shown in FIGS. 1, 2 and 4, a vertical engine output shaft 2 a isextended downward from engine 2 through opening 1 e, and fixedlyprovided thereon with a traveling power output pulley 2 b belowhorizontal plate 1 a of body frame 1. Engine output shaft 2 a is furtherextended downward from traveling power output pulley 2 b and provided ona bottom end thereof with a working power output pulley 2 d. A PTOsolenoid clutch 2 c is provided on the bottom end portion of engineoutput shaft 2 a and drivingly interposed between traveling power outputpulley 2 b and working power output pulley 2 d.

As shown in FIGS. 1 and 4, a bonnet 9F is disposed over a front portionof body frame 1 so as to enclose engine 2. A steering wheel 6 isextended upward from a rear end portion of bonnet 9F. A speed changingpedal 7 for changing the traveling speed and direction of the vehicle isdisposed at a rear bottom portion of bonnet 9F behind engine 2. In thisvehicle, speed changing pedal 7 is seesaw-like shaped so as to include afront depression plate 7 a for setting variable forward traveling speed,and a rear depression plate 7 b for setting variable backward travelingspeed. Alternatively, individual pedals for respective changes in theforward traveling speed and in the backward traveling speed can beprovided.

As shown in FIGS. 1 and 4, horizontal plate 1 a is stepped at afore-and-aft intermediate portion so as to have a higher rear portionwith a vertically penetrating opening 1 c shown in FIGS. 2, 3 and 5. Arear transaxle housing 10 of a rear (main) transaxle RT is verticallypassed through opening 1 c. In this regard, rear transaxle housing 10 isformed by vertically joining an upper half 10 a and a lower half 10 b toeach other through a horizontal joint surface. The horizontal jointsurface between upper and lower halves 10 a and 10 b is leveled with theupper surface of the higher rear portion of horizontal plate 1 a of bodyframe 1. Upper half 10 a is formed integrally with left and right shaftsupport portions 10 c, which are extended laterally distally from leftand right ends of opening 1 c, when viewed in plan as shown in FIG. 2.Each of shaft support portions 10 c is thickened at the distal endthereof so as to serve as bosses. The bosses whose bottom surfacescontact the upper surface of horizontal plate 1 a are fastened tohorizontal plate 1 a by bolts 11. Further, as shown in FIG. 2,horizontal plate 1 a of body frame 1 is formed integrally with a tab 1 dextended rearward from a front edge of opening 1 c, and a boss 10 dprojecting forward from a front bottom edge of upper half 10 a isfastened onto tab 1 d through a bolt 12, so as to receive a countertorque caused in rear transaxle housing 10 during traveling of thevehicle.

As shown in FIGS. 1 to 5, left and right final transmission devices 40are disposed on respective lateral opposite sides of the higher rearportion of body frame 1 so as to be drivingly interposed between reartransaxle RT and rear wheels 3. Each of final transmission devices 40includes a transmission casing 41 fixed onto an outer surface of each ofleft and right vertical side plates 1 b. A top portion of eachtransmission casing 41 projects upward from horizontal plate 1 a of bodyframe 1 so as to journal an output shaft 30 projecting from each shaftsupport portion 10 c of rear transaxle housing 10. Each of transmissioncasings 41 is extended downward so as to journal an axle 3 a of each ofrear wheels 3 at a bottom portion thereof.

As shown in FIGS. 1 and 4, a rear cover 9R is disposed over the rearportion of body frame 1 so as to enclose rear transaxle RT. A driver'sseat 8 is mounted on rear cover 9R.

As shown in FIGS. 1 to 5, a mower unit 5 is disposed below body frame 1.Mower unit 5 includes a mower deck 5 a incorporating rotary blades 5 bdisposed between rear wheels 3 and front wheels 4. Mower unit 5 includesa grass-discharging duct 5 e, which is extended rearward from mower deck5 a between left and right rear wheels 3, and projects rearward from arear end of body frame 1. The lateral width of grass-discharging duct 5e is set close to the lateral distance between left and righttransmission casings 41, and the left and right ends ofgrass-discharging duct 5 e are equally spaced from the respective leftand right transmission casings 41. Mower unit 5 may include a blower forblowing grass mowed by rotary blades 5 b outward from grass-dischargingduct 5 e. A grass collection box (not shown) can be attached onto therear end of body frame 1 so as to collect grass mowed by rotary blades 5b through grass-discharging duct 5 e.

As shown in FIGS. 1 and 4, a front end portion of mower deck 5 a is hungdown through a mower link 5 f from a mower bracket 1 h extended downwardfrom a front end of body frame 1. Lift arms 5 g of a mower liftmechanism, having base ends pivoted on body frame 1, are pivotallyconnected to a rear portion of mower deck 5 a, and driven by anactuation for raising and lowering mower deck 5 a.

As shown in FIGS. 1 and 4, mower deck 5 a supports a vertical mowerinput shaft 5 c drivingly connected to rotary blades 5 b and the blower.Mower input shaft 5 c projects upward from mower deck 5 a, and isfixedly provided thereon with a mower input pulley 5 d, which isdrivingly connected to working power output pulley 2 d on engine outputshaft 2 a through a belt 15, thereby driving rotary blades 5 b by powerof engine 2.

As shown in FIGS. 1 and 3 to 5, a vertical input shaft 20 of reartransaxle RT is extended downward from a bottom of rear transaxlehousing 10 into a space just above grass-discharging duct 5 e, and isfixedly provided thereon with an input pulley 20 a, which is drivinglyconnected to traveling power output pulley 2 b on engine output shaft 2a through a belt 13, thereby driving rear wheels 3 by power of engine 2through rear transaxle RT and final transmission devices 40. As shown inFIG. 2, a belt 13 is looped over a pulley 13 a between pulleys 2 b and20 a so as to be tensed.

As shown in FIGS. 1 and 4, a front end portion of body frame 1 in frontof engine 2 is formed into a bracket 1 f having a fore-and-afthorizontal center pin 1 g. Muffler 2 g extended forward from engine 2 issecured on bracket 1 f. A front transaxle housing 60 of a front(auxiliary) transaxle FT is pivoted at a lateral center portion thereofon center pin 1 g so as to be vertically swingable at left and rightends thereof. As shown in FIG. 2, left and right steering units 61support respective axles 4 a of left and right front wheels 4, and aresteerably attached to the respective left and right ends of fronttransaxle housing 60, so that left and right front wheels 4 serve assteerable wheels.

As shown in FIG. 2, a steering arm 64 is fixed on a top portion of oneof steering units 61. A steering link rod 65 operatively connected tosteering wheel 6 (through a power steering mechanism) is pivoted at afront end thereof onto steering arm 64. A tie rod 66 is pivotallyinterposed between left and right steering units 61. Therefore, left andright steering units 61 with respective front wheels 4 are steeredaccording to the turning direction and angle of steering wheel 6.

Left and right individual output shafts 60 b, shown in FIGS. 1 and 4,are supported in front transaxle housing 60, and each of output shafts60 b is drivingly connected to each of front wheels 4 through adeceleration mechanism in each of steering units 61. As shown in FIG. 2,left and right hydraulic motors M2 are disposed in front transaxlehousing 60, so as to drive respective output shafts 60 b, therebyindividually (differentially) driving respective front wheels 4. Asshown in FIGS. 1 and 4, a pair of ports 10 f are provided on a side ofrear transaxle housing 10 (lower half 10 b), and a pair of ports 60 aare provided on a rear surface of front transaxle housing 60. A pair ofhydraulic pressure fluid pipes 14 are interposed between ports 10 f andports 60 a, so as to supply hydraulic motors M2 with hydraulic pressurefluid from rear transaxle housing 10 (i.e., a later-discussed hydraulicpump P in rear transaxle housing 10 serves as a hydraulic pressuresource of hydraulic motors M2).

Hydraulic motors M2 are fluidly connected to hydraulic pump P inparallel, so that they can output differentially. At least one ofhydraulic motors M2 is a variable displacement hydraulic motor with acam mechanism 62 for changing the displacement according to turning offront wheels 4. In this regard, cam mechanism 62 is provided on the rearsurface of front transaxle housing 60, and a detection link rod 63 ispivoted at one end thereof onto one of left and right steering units 61(preferably, other than steering unit 61 with steering arm 64), andextended to be operatively connected to cam mechanism 62, so as toreduce the displacement of variable displacement hydraulic motor M2according to an increase of the turning angle of corresponding steeringunit 61. Consequently, during turning of the vehicle, the peripheralspeed of front wheels 4 is increased larger than the peripheral speed ofrear wheels 3 so as to prevent front wheels 4 from being dragged.

A traveling power transmission system around grass-discharging duct 5 ewill be described with reference to FIGS. 1 to 5. Due to rear transaxleRT being disposed above grass-discharging duct 5 e, left and rightvertical side surfaces of grass-discharging duct 5 e are disposed closeto inner surfaces of left and right vertical side plates 1 b of bodyframe 1, i.e., left and right final transmission devices 40. No partexists in a narrow space between each of the left and right verticalsurfaces of grass-discharging duct 5 e and the inner surface of each ofleft and right side plates 1 b of body frame 1. Therefore, the lateralwidth of grass-discharging duct 5 e is close to the lateral width ofbody frame 1, so as to have a large volume in comparison with agrass-discharging duct disposed on one lateral side of a rear transaxle.

Grass-discharging duct 5 e has a top surface slanted upwardly rearwardso that the rear open end of grass-discharging duct 5 e has a largevertical width. In this regard, the diameter of input pulley 20 a on thebottom portion of input shaft 20 projecting downward from rear transaxlehousing 10 is smaller than the fore-and-aft width of the bottom portionof rear transaxle housing 10 (lower half 10 b), so that input pulley 20a is effectively disposed in the narrow dead space just above theupwardly rearward slanted top surface of grass-discharging duct 5 e.Consequently, the bottom portion of rear transaxle housing 10 becomes ashigh as possible so that the bottom portion of input shaft 20 with inputpulley 20 a projecting downward from rear transaxle housing 10 is alsoas high as possible, so as to increase the slant angle of the topsurface of grass-discharging duct 5 e, i.e., increase the vertical widthof the rear end of grass-discharging duct 5 e, thereby increasing thevolume of grass-discharging duct 5 e. In correspondence to the highposition of rear transaxle housing 10, as mentioned above, the rearportion of horizontal plate 1 a of body frame 1 having opening 1 c isstepped to be higher than the front portion of horizontal plate 1 a ofbody frame 1, so as to hold rear transaxle housing 10.

With respect to each of final transmission devices 40, as shown in FIGS.3 and 5, in transmission casing 41, a sprocket 42 is fixed on a distalend of output shaft 30, a sprocket 43 is fixed on a proximal end of axle3 a of rear wheel 3, and a chain 44 is looped over sprockets 42 and 43so as to transmit the rotation of output shaft 30 to rear wheel 3.Alternatively, each of final transmission devices 40 may be a belt typetransmission or a gear train.

The only different point between the first embodiment shown in FIGS. 1to 3 and the second embodiment shown in FIGS. 4 and 5 is a position of acooling fan 20 b on input shaft 20 of rear transaxle RT.

Referring to the first embodiment shown in FIGS. 1 to 3 and 7, a coolingfan 20 b is fixed on the lower portion of input shaft 20 projectingdownward from rear transaxle housing 10 (lower half 10 b) adjacent toinput pulley 20 a. Preferably, as shown in FIGS. 1, 3 and 7, cooling fan20 b is disposed just above input pulley 20 a so as to prevent coolingfan 20 b, which is diametrically larger (i.e., horizontally wider) thaninput pulley 20 a, from interfering with grass-discharging duct 5 etherebelow, and to ensure a large vertical width of grass-dischargingduct 5 e. Alternatively, cooling fan 20 b may be disposed below inputpulley 20 a. Further preferably, cooling fan 20 b according to the firstembodiment blows air upward so as to cool rear transaxle housing 10thereabove.

Referring to the second embodiment shown in FIGS. 4 and 5 and 8, a topportion of input shaft 20 projects upward from rear transaxle housing 10(upper half 10 a), and cooling fan 20 b is fixed on the top portion ofinput shaft 20 projecting upward from rear transaxle housing 10vertically opposite to input pulley 20 a disposed below rear transaxlehousing 10. Preferably, cooling fan 20 b according to the secondembodiment blows air downward so as to cool rear transaxle housing 10therebelow. This downward air flow prevents mowed and spread grass fromentering a vehicle body above body frame 1, thereby keeping the interiorof the vehicle body clean.

Alternatively, a pair of upper and lower cooling fans may be provided onupper and lower portions of input shaft 20 projecting upward anddownward from rear transaxle housing 10, respectively. In thisstructure, the lower cooling fan blows air upward through opening 1 caround rear transaxle housing 10, and the upper cooling fan blows airdownward and returns the air blown upward from the lower cooling fan soas to enhance the effect of cooling rear transaxle housing 10.

An inner structure of rear transaxle housing 10 shown in FIGS. 6 to 9 iscommon between the first and second embodiments, while the position ofcooling fan 20 b shown in FIG. 7 is different from that shown in FIG. 8.The common inner structure of rear transaxle housing 10 shown in FIGS. 6to 9 will be described.

A side cover 10 e, supporting a pivot shaft (later-discussed trunnion)16 a of a speed control arm 17 and a retaining pin 18, is fixed ontomutually joined upper and lower halves 10 a and 10 b so as to completerear transaxle housing 10. Rear transaxle housing 10 is filled thereinwith fluid (serving as lube for gears and as hydraulic pressure fluidfor an HST), so as to serve as a fluid sump. An inner space of reartransaxle housing 10 is divided into an HST chamber C1 and a gearchamber C2 by a vertical partition wall formed of vertically joinedupper and lower halves 10 a and 10 b.

HST chamber C1 incorporates an HST (hydrostatic transmission) includinga hydraulic pump P, a hydraulic motor M1 and a center section 21. Gearchamber C2 incorporates left and right output shafts 30, a differentialgear unit 33 disposed between left and right output shafts 30, and adeceleration gear train 31 drivingly interposed between hydraulic motorM1 and differential gear unit 33.

A fluid filter 52, e.g., a magnet disk, is fitted in an opening formedin the partition wall so as to remove impurities, such as metal powdercaused by rubbing of gears, from fluid in gear chamber C2 before thefluid enters HST chamber C1 through the opening.

A structure of the HST will be described with reference to FIGS. 6 to 9.Center section 21 is fixed in HST chamber C1. Center section 21 includesan upward horizontal pump mounting surface and a vertical motor mountingsurface. When viewed in plan, the vertical motor mounting surface isextended perpendicular to the longitudinal direction of output shafts30, and disposed opposite to output shafts 30 with respect to the pumpmounting surface. Center section 21 rotatably supports vertical input(pump) shaft 20 at the center of the horizontal pump mounting surface,and rotatably supports a horizontal motor shaft 23 disposed at thecenter of the vertical motor mounting surface in parallel to outputshafts 30.

Hydraulic pump P includes a cylinder block Pa relatively unrotatablyengaged on input shaft 20 (serving as a pump shaft) and slidablyrotatably fitted onto the pump mounting surface of center section 21.Vertical pistons Pb are disposed around input shaft 20 and reciprocallymovably fitted into cylinder block Pa. A trunnion type movable swashplate 16 is disposed above cylinder block Pa and pressed against headsof pistons Pb. Movable swash plate 16 has a pair of opposite trunnionshafts 16 a disposed in parallel to output shafts 30. One of trunnionshafts 16 a is rotatably supported by the partition wall portion ofupper half 10 a of rear transaxle housing 10, and the other of trunnionshafts 16 a is rotatably supported by side cover 10 e. In this way,movable swash plate 16 is rotatable around trunnion shafts 16 a.

Input shaft 20 is passed through a central opening of movable swashplate 16, and is journalled in a cylindrical support portion formed on atop of upper half 10 a of rear transaxle housing 10 through a bearing.In the first embodiment, as shown in FIG. 7, the top of input shaft 20ends in the cylindrical support portion of upper half 10 a of reartransaxle housing 10, and a cap 59 closes the top opening of thecylindrical support portion above the top of input shaft 20. In thesecond embodiment, as shown in FIG. 8, the top opening of thecylindrical support portion is not closed by cap 59, and the top portionof input shaft 20 projects upward from the top opening so as to befixedly provided thereon with cooling fan 20 b.

Speed control arm 17 is fixed on a distal end of trunnion shaft 16 aoutside of side cover 10 e, and operatively connected to above-mentionedspeed changing pedal 7. In rear transaxle housing 10, a neutralreturning spring 19 is wound around trunnion shaft 16 a supported byside cover 10 e. Both end portions of spring 19 are twisted, cross eachother, and are extended. A push pin 16 b fixed to movable swash plate 16and retaining pin 18 fixed to side cover 10 e are disposed between theextended end portions of spring 19.

When speed changing pedal 7 is disposed at its neutral position, movableswash plate 16 is disposed at its neutral position, and the both ends ofspring 19 press and pinch pins 16 a and 18 therebetween so as to holdmovable swash plate 16 at the neutral position determined by retainingpin 18. When either front or rear depression plate 7 a or 7 b of speedchanging pedal 7 is depressed, movable swash plate 16 rotates in one ofopposite directions from the neutral position, whereby push pin 16 bpushes one end of spring 19 away from the other end of spring 19retained by retaining pin 18 so as to cause a force of spring 19 biasingmovable swash plate 16 toward the neutral position. Therefore, whenspeed changing pedal 7 is released from the depression, movable swashplate 16 and speed changing pedal 7 return to their respective neutralpositions swiftly.

Retaining pin 18 is an eccentric shaft, and normally fastened at anouter threaded end portion thereof onto an outer surface of side cover10 e by a nut. When the neutral position of movable swash plate 16 isdeviated from the neutral position of speed changing pedal 7 and speedcontrol arm 17, the nut is loosened and retaining pin 18 is rotated soas to correct the deviation of the neutral position.

Hydraulic motor M1 includes a cylinder block M1 a relatively unrotatablyengaged on motor shaft 23 and slidably rotatably fitted onto the motormounting surface of center section 21. Horizontal pistons M1 b aredisposed around motor shaft 23 and reciprocally movably fitted intocylinder block M1 a. A fixed swash plate 22 is fixed onto the partitionwall in rear transaxle housing 10 and pressed against heads of pistonsM1 b. Motor shaft 23 is passed through a central opening of fixed swashplate 22, and is journalled by the partition wall through a bearing soas to project into gear chamber C2.

In center section 21, a pair of kidney ports are opened at the pumpmounting surface, and a pair of kidney ports are opened at the motormounting surface. Center section 21 is formed therein with a pair ofupper and lower parallel horizontal fluid holes 21 a and 21 b extendedperpendicular to output shafts 30 when viewed in plan. Upper fluid hole21 a is opened to one kidney port at the pump mounting surface and toone kidney port at the motor mounting surface. Lower fluid hole 21 b isopened to the other kidney port at the pump mounting surface through avertically slant fluid hole 21 c extended in parallel to output shafts30 when viewed in plan, and is extended longer than upper fluid hole 21a so as to be opened to the other kidney port at the motor mountingsurface.

A motor output gear 23 a and a brake disk 23 b are fixed on motor shaft23 in gear chamber C2. Brake disk 23 b is disposed between brake shoes26 and 27. A vertical brake operation shaft 24 is rotatably supported byrear transaxle housing 10, and formed with a cam surface facing brakeshoe 26. A top portion of brake operation shaft 24 projects upward fromrear transaxle housing 10 so as to be fixedly provided thereon with abrake arm 25. A brake operation device (not shown), e.g., a brake pedaldisposed adjacent to speed changing pedal 7 shown in FIGS. 1 and 4, isoperatively connected to brake arm 25. When the brake operation deviceis operated for braking (the brake pedal is depressed), brake operationshaft 24 is rotated so as to slant the cam surface thereof against brakeshoe 26, so as to press brake shoe 26 against brake disk 23 b, i.e.,press brake disk 23 b between brake shoes 26 and 27, thereby brakingmotor shaft 23, whereby left and right output shafts 30, and left andright rear wheels 3 are stopped.

Referring to FIG. 6, a horizontal counter shaft 32 is journalled in gearchamber C2, and disposed in parallel to output shafts 30. Adiametrically small and axially long gear 32 b is fixed on counter shaft32. A diametrically large gear 32 a is relatively unrotatably fitted ona portion of diametrically small gear 32 b, and meshes with motor outputgear 23 a. The remaining portion of diametrically small gear 32 b mesheswith a bull gear 34 of differential gear unit 33. In this way, the geartrain between motor shaft 23 and bull gear 34 through counter shaft 32serves as two-stepped deceleration gear train 31.

Referring to FIG. 6, in differential gear unit 33, proximal ends ofoutput shafts 30 are relatively rotatably fitted into a center axialhole bull gear 34. A pinion 35 is pivoted in bull gear 34, so as to havea pivot axis disposed radially of bull gear 34. Differential side gears36 are fixed on respective output shafts 30, disposed along respectiveleft and right side surfaces of bull gear 34, and mesh with pinion 35.

Referring to FIG. 6, differential gear unit 33 is provided with adifferential lock mechanism 37. Differential lock mechanism 37 includesa differential lock slider 38 axially slidably fitted on one of outputshafts 30. A portion of differential lock slider 38 is constantly andslidably fitted in bull gear 34. Differential lock slider 38 isselectively engaged or disengaged into and from a recess formed on aback surface of differential side gear 36 fixed on the one of outputshafts 30, depending on the axial slide on output shaft 30. A horizontaldifferential lock shaft 51 is disposed in parallel to output shafts 30,and journalled by rear transaxle housing 10 (lower half 10 b).Differential lock slider 38 is connected to differential clutch slider38 through a fork 39. A differential lock arm 50 is fixed on an outerend of differential lock shaft 51 outside rear transaxle housing 10, asshown in FIGS. 3, 5 and 6.

Differential lock arm 50 is operatively connected to a differential lockoperation device (not shown), such as a pedal disposed adjacent todriver's seat 8, which is switchable between a differential position anda differential lock position. When the differential lock operationdevice is disposed at the differential position, differential lockslider 38 is disengaged from differential side gear 36 so as to allowoutput shafts 30 to differentially rotate. When the differential lockoperation device is disposed at the differential lock position,differential lock slider 38 is engaged with differential side gear 36 soas to lock output shafts 30 to each other through bull gear 34, therebypreventing output shafts 30 from differentially rotating.

Referring to FIG. 7 or 8 and FIG. 9, a charge pump 55 and a structuretherearound will be described. A pair of charge check valves 53 arefitted in respective upper and lower fluid holes 21 a and 21 b in centersection 21. A top surface of a charge pump casing 54 is fixed to ahorizontal bottom surface of center section 21. Center section 21 isformed with a pump chamber recessed downward from the top surface. Aninner rotor 55 a and an outer rotor 55 b are disposed in the pumpchamber so as to constitute trochoidal charge pump 55. Inner rotor 55 ais fixed on input shaft 20 extended downward from center section 21, andouter rotor 55 b meshing with inner rotor 55 a rotates on its own axisin charge pump casing 54 according to the rotation of inner rotor 55 atogether with input shaft 21.

A delivery port of charge pump 55 is connected to a bottom opening of acharge fluid port formed in center section 21 at the bottom surface ofcenter section 21, and the charge fluid port is connected to fluid holes21 a and 21 b through respective charge check valves 53. In this way,fluid delivered from charge pump 55 is supplied into hydraulicallydepressed one of fluid holes 21 a and 21 b through opened correspondingcharge check valve 53.

Charge pump casing 54 has formed therein a suction port extendeddownward from the pump chamber and has an opening horizontally outwardto the fluid sump in rear transaxle housing 10. An outer wall of lowerhalf 10 b of rear transaxle housing 10 is bored by a horizontallypenetrating hole facing the opening of the suction port. The hole isplugged by a cap 57, and a horizontal cylindrical fluid filter 56 isdisposed between cap 57 and the opening of the suction port. Fluidfilter 56 is inserted or removed into and from rear transaxle housing 10through the hole from which cap 57 is removed. A spring 58 is interposedbetween fluid filter 56 and cap 57 so as to press and fit fluid filter56 onto charge pump casing 54. In this way, charge pump 55 absorbs fluidfrom the fluid sump in rear transaxle housing 10 through fluid filter56.

An alternative structure of charge pump 55 in rear transaxle housing 10will be described with reference to FIG. 10. A charge pump casing 70 isnot fixed to center section 21. Charge pump casing 70 is formed with apump chamber recessed downward from a top surface thereof. Inner andouter rotors 55 a and 55 b, constituting trochoidal charge pump 55, arerotatably slidably fitted into the pump chamber. Top surfaces of innerand outer rotors 55 a and 55 b project upward from the top surface ofcharge pump casing 54 and rotatably slidably abut against the horizontalbottom surface of center section 21.

A compressed spring 71 is interposed between a bottom surface of chargepump casing 70 and a bottom wall of lower half 10 b of rear transaxlehousing 10 so as to bias charge pump casing 70 upward, thereby slidablyand rotatably pressing the top surfaces of inner and outer rotors 55 aand 55 b against the horizontal bottom surface of center section 21. Thecharge pressure of charge pump 55 is defined by the biasing force ofspring 71 so that excessive pressure of fluid delivered from charge pump55 expands a gap between the top surfaces of rotors 55 a and 55 b andthe bottom surface of center section 21 and the fluid of the excessivepressure leaks through the gap into the fluid sump in rear transaxlehousing 10.

A vertical cylindrical fluid filter 72 is interposed between the bottomsurface of center section 21 and the bottom wall of lower half 10 b ofrear transaxle housing 10, and disposed around charge pump 55 and chargepump casing 70, so that fluid is supplied to charge pump 55 from thefluid sump in rear transaxle housing 10 through fluid filter 72 and afluid passage formed in charge pump casing 70. Charge pump 55 suppliesfluid to either fluid hole 21 a or 21 b through corresponding chargecheck valve 53, similar to charge pump 55 shown in FIG. 9.

Rear transaxle housing 10 is provided with ports 10 f (shown in FIGS. 1and 4, and not shown in FIGS. 6 to 10) for supplying fluid to hydraulicmotors M2 in front transaxle FT. Center section 21 is formed so as tofluidly connect the HST closed circuit, i.e., fluid holes 21 a, 21 b and21 c between hydraulic pump P and motor M1, to ports 10 f.

It is further understood by those skilled in the art that the foregoingdescription is a preferred embodiment of the disclosed apparatus andthat various changes and modifications may be made in the inventionwithout departing from the scope thereof defined by the followingclaims.

1. A transaxle for a lawn tractor, the lawn tractor including a primemover, a mower unit, a grass-discharging duct extended from the mowerunit at a substantially lateral center portion of the lawn tractor, leftand right drive wheels having respective axles disposed on lateralopposite sides of the grass-discharging duct, and left and right finaltransmission devices disposed on lateral opposite sides of thegrass-discharging duct, the transaxle comprising: a transaxle housingdisposed above the grass-discharging duct, wherein the left and rightfinal transmission devices are connected at upper portions thereof torespective left and right ends of the transaxle housing; an input shafthaving a lower portion extended downward from the transaxle housing; aninput pulley for receiving power from the prime mover, wherein the inputpulley is provided on the lower portion of the input shaft so as to bedisposed between the transaxle housing and the grass-discharging duct;and left and right output shafts projecting laterally from the transaxlehousing opposite to each other above the grass-discharging duct, whereinthe axles of the left and right drive wheels are disposed below therespective left and right output shafts on respective left and rightsides of the grass-discharging duct, wherein the left final transmissiondevice is interposed between the left output shaft and the axle of theleft drive wheel on the left side of the grass-discharging duct, andwherein the right final transmission device is interposed between theright output shaft and the axle of the right drive wheel on the rightside of the grass-discharging duct.
 2. The transaxle according to claim1, further comprising: a hydraulic pump disposed in the transaxlehousing so as to be driven by rotating the input shaft; and a hydraulicmotor disposed in the transaxle housing so as to be fluidly connected tothe hydraulic pump and to drive the left and right output shafts.
 3. Thetransaxle according to claim 1, further comprising: a cooling fanprovided on the lower portion of the input shaft so as to be disposedbetween the transaxle housing and the grass-discharging duct.
 4. Thetransaxle according to claim 1, wherein the input shaft has an upperportion extended upward from the transaxle housing, and wherein acooling fan is provided on the upper portion of the input shaft so as tobe disposed above the transaxle housing.
 5. A lawn tractor comprising: aprime mover; a mower unit; a grass-discharging duct extended from themower unit at a substantially lateral center portion of the lawntractor; left and right drive wheels having respective axles disposed onlateral opposite sides of the grass-discharging duct; left and rightfinal transmission devices disposed on lateral opposite sides of thegrass-discharging duct; and a transaxle disposed above thegrass-discharging duct, wherein the transaxle comprises: a transaxlehousing; an input shaft having a lower portion extended downward fromthe transaxle housing; an input pulley for receiving power from theprime mover, wherein the input pulley is provided on the lower portionof the input shaft so as to be disposed between the transaxle housingand the grass-discharging duct; and left and right output shaftsprojecting laterally from the transaxle housing opposite to each otherabove the grass-discharging duct, wherein the axles of the left andright drive wheels are disposed below the respective left and rightoutput shafts on respective left and right sides of thegrass-discharging duct, wherein the left final transmission device isinterposed between the left output shaft and the axle of the left drivewheel, and wherein the right final transmission is interposed betweenthe right output shaft and the axle of the right drive wheel.
 6. Thelawn tractor according to claim 5, further comprising: a hydraulic pumpdisposed in the transaxle housing so as to be driven by rotating theinput shaft; and a hydraulic motor disposed in the transaxle housing soas to be fluidly connected to the hydraulic pump and to drive the leftand right output shafts.
 7. The lawn tractor according to claim 5,further comprising: a cooling fan provided on the lower portion of theinput shaft so as to be disposed between the transaxle housing and thegrass-discharging duct.
 8. The lawn tractor according to claim 5,wherein the input shaft has an upper portion extended upward from thetransaxle housing, and wherein a cooling fan is provided on the upperportion of the input shaft so as to be disposed above the transaxlehousing.
 9. A lawn tractor comprising: a frame; a prime mover mountedupward from the frame and having an output shaft and an output pulley onthe output shaft below the frame; a mower unit disposed below the frame;a grass-discharging duct extended from the mower unit at a substantiallylateral center portion of the tractor below the frame; left and rightdrive wheels disposed on lateral opposite sides of the frame and onlateral opposite sides of the grass-discharging duct; and a transaxlesupported by the frame and disposed above the grass-discharging duct,wherein the transaxle comprises: a transaxle housing; an input shafthaving a lower portion extended downward from the transaxle housing; aninput pulley provided on the lower portion of the input shaft so as tobe disposed between the lowest end of the transaxle housing and thegrass-discharging duct and to be drivingly connected to the outputpulley of the prime mover through a belt disposed below the frame; andleft and right output shafts projecting laterally from the transaxlehousing opposite to each other so as to be drivingly connected to therespective left and right drive wheels.
 10. The lawn tractor accordingto claim 9, further comprising: a hydraulic pump disposed in thetransaxle housing so as to be driven by rotating the input shaft; and ahydraulic motor disposed in the transaxle housing so as to be fluidlyconnected to the hydraulic pump and to drive the left and right outputshafts.
 11. The lawn tractor according to claim 9, further comprising: acooling fan provided on the lower portion of the input shaft so as to bedisposed between the transaxle housing and the grass-discharging duct.12. The lawn tractor according to claim 9, wherein the input shaft hasan upper portion extended upward from the transaxle housing, and whereina cooling fan is provided on the upper portion of the input shaft so asto be disposed above the transaxle housing.